The present invention relates generally to electrical filter systems and more particularly to an adaptive, electrical filter system for an electric actuator used in positioning process-controlling elements.
In the industrial processing environment, process-controlling elements, such as dampers and vanes, are generally required to be controllable to provide a means for adjusting the flow of fluid material through industrial ducting. In the past, pneumatic control of damper or vane actuators was practiced extensively, but in recent times electrically controlled actuators are used more often. The electrically controlled actuators employ electric motors, generally AC, to drive the actuators and have gained acceptability largely on account of the efficient, responsive control available therewith.
A problem has persisted with the electrical actuators, however, which heretofore has defied any practical solution. That problem concerns itself with spurious noise generally associated with an error signal used for varying the position of the damper or vane. Generally speaking, all electric actuators employ what is most commonly referred to as a closed-loop feedback control system whereby an error signal generated by a process-sensitive transducer is introduced into the loop whenever one or more of the parameters being monitored determines that a change in the fluid flow through the ducting is required. The error signal introduced into the loop is used to activate the control of an AC motor which causes the damper or vane to change its physical position within the ducting in order to null the error signal. Unfortunately, however, even in those instances where no error signal is intended to be generated, noise associated with the necessarily high gain loop causes constant energization and deenergization of the motor leading to unnecessary motor heating and gear wear as well as gross inefficiency in operation.
In the past, the problems associated with a noisy loop were avoided by merely decreasing the gain of the loop or increasing the dead band. In general, this avoided the problem of constant motor energization and deenergization, but greatly decreased the sensitivity of the control circuit. Other prior art attempts at decreasing the effects of the noise associated with the loop have included various reactive filter networks interposed within the loop, all of which methods provided less sensitive control of the actuator.